Airworthiness Directives; Sikorsky Aircraft Corporation (Sikorsky) Helicopters

We are adopting a new airworthiness directive (AD) for Sikorsky Model S-70, S-70A, S-70C, S-70C (M), and S-70C (M1) helicopters with General Electric (GE) T700-GE-401C or T700-GE-701C engines installed. This AD requires establishing new fatigue life limits for certain GE engine gas generator turbine (GGT) rotor parts. This AD was prompted by a reevaluation of the method for determining the life limit for certain GE engine GGT rotor parts and the determination that these life limits should be based on low cycle fatigue (LCF) events instead of hours time-in-service (TIS). The actions are intended to prevent fatigue failure of a GGT rotor part, engine failure, and subsequent loss of control of the helicopter.